kWh to kW Calculator

A kilowatt-hour counts energy, a kilowatt counts speed

A kilowatt-hour is a unit of energy: one kilowatt of power held for one hour. A kilowatt is a unit of power: how fast energy is flowing at any moment. The two sit one step apart, and the step always involves time. The NIST conversion tables list the kilowatt-hour as 3.6 megajoules, an amount of energy, while the watt is defined as one joule per second, a rate.

That rate-versus-amount split is the whole story:

• kW = kWh ÷ hours. Divide the energy by the time it was spread over and the result is the average power.
• kWh = kW × hours. Multiply a steady power by the time it runs and the result is the energy.

A quick pair of examples. A 1,500 W space heater runs for 4 hours: 1.5 kW × 4 h = 6 kWh of energy. Pushing those 6 kWh back the other way, 6 ÷ 4 = 1.5 kW, recovers the heater rating. Nothing was created or lost; the hours just crossed the divide sign. Every example on this page follows that same round trip, and the calculator does it for you in both directions.

The hours you divide by, and the periods people use

The arithmetic is one division, but picking the right divisor decides whether the answer means anything. A 30-day month holds 720 hours, a 31-day month holds 744, the average month over a year works out to 730, and a year holds 8,760 hours. Match the divisor to the number you are converting:

That 730 figure comes from 365 × 24 = 8,760, then 8,760 ÷ 12 = 730. Real utility bills run from 28 to 35 days depending on when the meter was read, so read the dates printed on the bill before you commit to a divisor.

By the numbers: a monthly bill turned into an average load

Take a bill showing 900 kWh for a 30-day month. The hours are 30 × 24 = 720. The average power is 900 ÷ 720 = 1.25 kW. That is the pace the whole house ran at, around the clock, for the month. It feels small next to a 200 amp service panel, and that gap is exactly the point of the next sections.

The national numbers line up. The EIA reports that the average US residential customer bought 10,791 kWh in 2022, and spreading that over a year gives 10,791 ÷ 8,760 = 1.23 kW. Houses across the country average out to a bit more than one kilowatt, all day, every day.

Money from the same numbers: at the 2025 US residential average of 17.30 cents per kWh, from the EIA Electric Power Monthly, Table 5.3, the 900 kWh month costs 900 × 17.30 = 15,570 cents, or $155.70. The average household bill works out to 10,791 × 0.173 = $1,866.84 for the year.

Two things follow from that. First, an energy reading says nothing about the moment the energy moved: 900 kWh in a month tells you the total and nothing about whether it arrived in one evening burst or spread evenly. That gap between a total and a peak is what this calculator closes when you divide by the hours. Second, the utility may also keep a demand register, the highest average it saw over a short window in the billing period, and that number, not your kWh total, is what a demand charge is built on.

So when a bill offers both a kWh total and a demand figure, read them as two different questions. The kWh total answers how much you used. The demand figure answers how hard you pulled at the worst moment, and it is the one that decides whether your panel, your inverter or your backup set is big enough.

By the numbers: an EV on a home charger

An electric car turns kWh to kW arithmetic into a nightly habit. Say the battery is 60 kWh and you drive it down to 20 percent, then charge back to 80 percent overnight. The energy moved is 0.6 × 60 = 36 kWh. Spread over an 8-hour session, 36 ÷ 8 = 4.5 kW of average charging power. A full 60 kWh refill in the same 8 hours would need 60 ÷ 8 = 7.5 kW.

The circuit decides what is possible. A Level 2 charger on a 240 volt, 40 amp circuit delivers 240 × 40 = 9,600 W, or 9.6 kW, so a full 60 kWh pack takes 60 ÷ 9.6 = 6.25 hours. If your session is longer than that, the car was probably not empty; a 60 kWh pack on a 9.6 kW charger for 8 hours could theoretically move 9.6 × 8 = 76.8 kWh, more than the battery holds.

One honest adjustment: charging is not perfect. Some of the wall energy becomes heat in the charger and cables, so the kWh at the meter read higher than the kWh stored in the pack. The average kW at the wall is therefore slightly above the battery-side math.

Charging speed also depends on what the car will accept. A vehicle with a 7.4 kW onboard charger cannot use a 9.6 kW wall unit at full output, so the session runs at the lower number and the hours stretch: 60 ÷ 7.4 = 8.11 hours for the same pack. Check both ratings before buying hardware, because the bottleneck decides the overnight result.

By the numbers: solar production and a home battery

Solar output makes the same trip in the other direction. A rooftop array that produced 30 kWh over a sunny day, in a location that gets about 5 peak sun hours, averaged 30 ÷ 5 = 6 kW during the hours it was producing. Run it in reverse: a 6 kW array under 5 sun hours yields 6 × 5 = 30 kWh for the day. The rest of the day it produces nothing, which is why the daily average is much smaller: 30 ÷ 24 = 1.25 kW across the full 24 hours.

Batteries do the same math at night. A 13.5 kWh home battery covering a 6-hour evening stretch averages 13.5 ÷ 6 = 2.25 kW. If the house wanted its full daytime average plus the evening peak from storage, the runtime would shrink: at 4.5 kW of draw the same 13.5 kWh lasts 13.5 ÷ 4.5 = 3 hours.

Both of these are averages with real limits behind them. The array also has an instantaneous cap, and the battery has a maximum discharge rate, so check those nameplate numbers before trusting an average that assumes more than the hardware allows.

Two arrays with the same kilowatt rating can still produce different daily totals. Roof pitch, the direction the panels face, shade from a chimney or a tree, and how dirty the glass gets all move the production figure, which is why a quote built on a nameplate number alone says little. Ask for the modeled annual production in kilowatt-hours instead, then divide by 8,760 if you want to compare it with the household average of 1.23 kW. Net metering adds a wrinkle: energy exported to the grid and credited back is counted by the meter in both directions, so a bill can show a small net total while the roof produced far more than the house used.

Average power is not peak power

The 1.25 kW average hides a lumpy reality. Big loads run for short stretches, and each one pulls far more than the average while it runs:

The dryer adds 81 kWh to the month, which averages out to 81 ÷ 720 = 0.11 kW, yet the moment it starts it pulls 5.4 kW, more than four times the whole house average. The ratio of average to peak is the load factor: for a house averaging 1.25 kW with a 5.4 kW peak, 1.25 ÷ 5.4 = 0.23.

Which number you need depends on the question. Average power sizes the bill and the solar offset. Peak power sizes the wires, the breaker and the generator, and some commercial rates add a demand charge built on the highest 15-minute average of the month, a number that has nothing to do with the kWh total.

Standby draw is the quiet part of the total. Clocks, routers, game consoles, televisions and chargers keep sipping while the house sleeps, and the sum can reach a few dozen kilowatt-hours a month without anything seeming to run. A plug-in metering gadget on each suspect outlet turns that guess into a number, and a switched strip clears several of them at once. Subtract the standby share from the monthly total before you divide, and the average that remains describes the loads you can schedule.

Reference table: energy over common periods

The same energy means a different power draw depending on the window. This table takes one kWh total and divides by each period:

Read one row across and the shape of the problem appears: 900 kWh squeezed into a single day would demand 37.5 kW, more than most houses can pull, while the same 900 kWh across a month asks for a gentle 1.25 kW. Time is the only thing that changed.

Time-of-use pricing makes the window matter in a second way. A tariff that charges more between 4 p.m. and 9 p.m. prices the same kilowatt-hour differently depending on when it lands, so shifting the dishwasher or the laundry into a cheaper window cuts the bill without changing the monthly total. The kWh on the bill stays put; the average draw moves to another part of the day, and an EV charger set to run overnight or a battery that charges after midnight does that shift on its own. Reading a rate schedule beside your interval data shows which hours carry the premium and how much load could move there.

Mistakes that make the answer wrong

Four errors account for most bad conversions between these two units:

• Dividing by days instead of hours. 900 ÷ 30 = 30, and calling that 30 kW overstates the load by a factor of 24. The divisor is always hours.
• Using 720 for every month. For a 31-day month the divisor is 744: 900 ÷ 744 = 1.21 kW, not 1.25. Small, but it compounds when you compare months.
• Mixing Wh and kWh. A device rated 500 Wh holds 0.5 kWh. Forgetting the factor of 1,000 makes the result wrong by exactly 1,000.
• Trusting the average to size hardware. An average of 1.25 kW is compatible with a 7.5 kW EV charger running nightly, and the breaker must be sized for 7.5 kW, not 1.25.

A fifth one shows up in spreadsheets: comparing a daily average from one home against a monthly average from another and concluding one house is greedy. Convert both to the same period first, or the comparison is noise.